Rabbit antibodies, labeled with 125I, have been produced that, after intravenous injection, are immunologically bound in rat tumors at levels of 2-4% of the injected dose in tumor equal to 1% of the rat weight. These tumors are induced by carcinogens in Fischer-344 rats and carried by transplant in this inbred strain of rat. Work will be directed at obtaining greater degrees of antibody localization. Also we will study the effects on tumor growth of purified unlabeled antibody, administered alone, and also combined treatment by irradiation and with therapeutic drugs.